This invention relates to a method of discharging suspended microparticles from a fluidic microsystem, in particular for discharging the microparticles from the microsystem, and a method for metering and/or treating of a microparticle flow output from a fluidic microsystem. This invention also relates to a microsystem designed for controlled discharge of suspended microparticles, and a discharge device for discharging suspended microparticles from a microsystem.
Fluidic microsystems for manipulation of biological or synthetic microparticles are known in general. The microsystems usually include one or more input channels, a channel arrangement for receiving and/or guiding fluids with suspended microparticles (e.g., biological cells) and one or more output channels. The channel arrangement has typical dimensions in the submillimeter range, e.g., approx. 100 to 500 μm. The suspended microparticles are characterized and/or manipulated electrically and/or optically, for example, in the channel arrangement. The suspension liquid with the microparticles has a freely adjustable flow velocity in the channel arrangement, which depends in particular on the manipulation and/or characterization steps implemented. Typical flow velocities are in the range of 10 mm/s or less. In conventional systems, connecting lines (so-called tubing) are connected to the output channels as the ends of the actual microsystem, in which connecting lines the microparticles are discharged from the respective outlet channel for further processing or collection or the like. These connecting lines typically have a length of approx. 2 to 8 cm. This corresponds to approx. 1 to 4 μl at an inner diameter of 254 μm, for example. A cell has essentially the same velocity in a connecting line as in manipulation in the channel arrangement and thus it needs a transit time of approx. 3 to 60 minutes from the outlet of the microsystem to the end of the connecting line, depending on the pump rates.
Such high transit times are unfavorable for reproducible further processing of the suspended microparticles. For example, considerably shorter times of approx. 10 to 60 seconds are needed for confirmed single-cell separation, as required for cloning cells. In addition, sedimentation phenomena which also play a role definitely reduce the cell recovery rate when the transit time is too long.
Rapid and reproducible discharge of suspended microparticles from microsystems, metering and/or treating of the oncoming flow of microparticles in transmission into subsequent systems is a problem that has not previously been solved at a justifiable technical expense.
The so-called enveloping flow principle of hydrodynamic focusing is known in fluid technology. Hydrodynamic focusing permits an alignment of specimen particles and, for certain analytical and preparative tasks, it allows particles and cells to be isolated (see A. Radbruch in Flow Cytometry and Cell Sorting, Springer Verlag, Berlin 1992). For implementation of the enveloping flow principle, a fluid flow with the particles is surrounded by an outer enveloping flow in a coaxial nozzle design. The enveloping flow must have a much greater velocity than the fluid flow so that hydrodynamic focusing may take place. The flow velocity of the enveloping flow is typically several thousand times greater than the flow velocity of the fluid. The fluid flow is entrained by the enveloping flow. The use of hydrodynamic focusing is limited to macroscopic laboratory equipment. It is not applicable in microsystem technology because due to the required high velocity of an enveloping flow, the flow conditions in the microsystem would also be influenced upstream relative to the aforementioned nozzle design. However, such an external and non-reproducible interference in flow conditions in the channel arrangement of a microsystem is not desirable.
Furthermore, there are known microstructured flow switches which are based on the enveloping flow principle (see G. Blankenstein in the publication “Microfabricated flow system for magnetic cell and particle separation” in Sci. & Clin. Appl. Magn. Carriers, eds. Häfeli et al., Plenum Press, New York, 1997). With a flow switch 10′ a specimen flow P is accompanied by a separate enveloping flow H in the channel arrangement of a microsystem, e.g., in a separation section 12′, as illustrated in FIG. 7. A magnetic separation device 11′ is provided on separation section 12′. Several outlet channels 14′ are connected to the separation section 12′, certain fractions of the specimen and enveloping flows being directed into these channels, depending on the function of separation device 11′. Use of the flow switch is limited to fluid convergence flows or fluid separations in the interior of the microsystem. The dimension of the output channels determines the parameters of the specimen and enveloping flows that can be added. The above-mentioned problem of discharging the suspended microparticles from microsystems cannot be solved with a flow switch.
The centering or deflection of a specimen flow is implemented with hydrodynamic focusing and the above-mentioned flow switches. However, the above-mentioned problem of extracting or focusing microparticle suspensions at the outlet of microsystems, i.e., in particular at the interface with macroscopic systems, is not solved in this way.